COVID-19 Spread Between Apartment Floors Through Failed Floor Drains
Key takeaway.
Nineteen residents of a five-story apartment building tested positive for SARS-CoV-2. Five patients had no direct contact with other infected residents but lived in vertically aligned apartments. Smoke experiments and genomic sequencing pointed to non-functioning floor drain traps as the likely route by which viral aerosols traveled upward through the drainage stack.
The study.
Han and colleagues investigated an unusual COVID-19 cluster in a residential apartment building where 19 residents tested positive for SARS-CoV-2. The epidemiological puzzle: five patients reported no direct contact with other residents, yet lived in apartments vertically aligned within the building. Traditional person-to-person transmission could not explain the pattern.
The investigation combined environmental sampling, whole-genome sequencing, and physical building evaluation. Smoke tracer experiments visualized air movement through the plumbing system, confirming that non-functioning floor drain traps allowed upward airflow through vertical drainage stacks. Cold ambient temperatures (-3.9 degrees C) exacerbated pressure differentials driving viral-laden aerosols upward. Environmental samples tested positive for SARS-CoV-2, and phylogenetic analysis found cases across multiple floors sharing a single viral strain, consistent with a common drain-mediated source the authors concluded possibly occurs.
This represented the first documented human transmission cluster attributed to drain trap failure-mediated aerosol transmission, establishing drain trap integrity as a critical infection control infrastructure requirement in multi-unit buildings.
Key findings.
- A single viral strain shared across floors Phylogenetic analysis identified one viral strain across multiple floors, which the authors concluded possibly spread through defective floor drain traps in vertically aligned apartments.
- Cold weather amplified pressure differentials Outdoor temperatures averaging -3.9 degrees C created significant pressure differentials driving upward air movement through drainage pipes, even in a five-story building.
- Smoke experiments confirmed the aerosol pathway Smoke tracer experiments visualized air movement through vertical drainage stacks and into residential units, confirming the transport pathway for viral particles.
- Environmental samples positive for SARS-CoV-2 Eight environmental samples tested positive, with drain-adjacent areas showing high viral RNA concentrations, establishing drains as contamination sources.
What this means for your facility.
This study provides the most direct evidence that failed floor drain traps cause disease transmission between building occupants. The affected residents had no contact with each other. Their only connection was shared drainage infrastructure with non-functioning trap seals. The implications extend beyond residential buildings to any multi-story facility: hotels, hospitals, dormitories, assisted living communities, and office buildings.
Green Drain's waterless one-way silicone valve holds its seal without retained water, so it is not subject to the evaporation-driven trap-seal failure described here. Unlike water-filled traps that can evaporate, freeze, or lose their seal through pressure transients, the one-way silicone valve maintains a consistent seal against upward air movement across all temperature ranges and pressure conditions. Each floor drain with a Green Drain installed restricts the upward air-and-aerosol pathway rather than leaving it open between units.
The Han study also highlights the speed at which drain-mediated transmission can occur. Once a trap seal fails, there is no warning and no detection mechanism. Green Drain's drop-in design enables rapid deployment across multi-unit buildings - an intervention that can be completed in hours rather than requiring the comprehensive plumbing reconstruction that many buildings would otherwise need.
Full citation.
Related research.
Protect your facility's drains.
Green Drain's waterless trap seal is a supportive engineering control that restricts the upward movement of air and aerosols, backed by independent bench testing. See how it works for your industry.